Precision drill for drilling noncircular bores

ABSTRACT

A precision drill for drilling noncircular bores, comprising a drill bit on a shaft and a holder for the workpiece being drilled, for providing a drill that can operate economically at high speeds. The workpiece holder oscillates translationally in at least one direction at a frequency controlled by the speed of the drill bit, and moves along a path determined by the desired shape of the bore to be drilled.

The invention relates to a precision drilling machine for drillingnoncircular bores according to the introductory part of patent claim 1.

Such precision drilling machines are known, for example from DE 38 18827 C; EP 0 430 984 B; and DE 43 12 937 A.

In connection with said drills, the drilling spindle with the rotatingbit, or only the drilling bit is periodically deflected as required whendrilling the form of the bore to be drilled. Practically, any desiredshape of bores can be drilled with said devices. Any shape of a bore islimited only by the technically possible kinetic dynamics of thedrilling spindle or the drilling bit support.

Devices, in connection with which the drilling spindle or the entiredrilling head is adjusted, only permit relatively low numbers ofrevolutions because of the relatively large masses to be moved.

Devices, in connection with which only a support of the drilling bit isdeflected within the drilling head, can operate with comparativelyhigher numbers of revolution. In the last-mentioned case, the support ofthe drilling bit, however, has only relatively little rigidity, whichimpairs the quality of the work.

Based on the facts outlined above, the invention deals with the problemof drilling noncircular bores with high working quality and with thehigh rotary speeds required for economical operation, in a superior wayand at more favorable cost than previously possible.

Said problem is solved with a design having the characteristic featuresof patent claim 1.

Deviating from the state of the art heretofore, the workpiece and notthe drilling bit or its support, or the spindle, is periodicallydeflected for drilling a non-circular drilling form in connection withsaid solution. This results in a simplification in that the periodicmotion of deflection needs not to be superimposed on a rotationalmotion, but rather represents the only form of motion for suchworkpiece.

The device according to the invention is particularly suitable fordrilling bores with an oval round shape. In this case, the workpieceonly has to run through one motion period with one rotation of thedrilling bit. This is explained in greater detail in the following byreference to a diagram. On the other hand, with each deflection of thedrilling bit the latter would have to run through two periods, i.e.,twice the number of periods during each rotation, which means that therotary speed applied in the work operation has to be kept ineconomically unfavorably low ranges, taking into account the limits inkinetic dynamics. For obtaining a bore with an oval basic shape, inconnection with which practically any oval, noncircular shapes areachievable up to the circumferential zone, through which the long ovalaxis extends, the tool has to oscillate translatorily only in onedirection.

According to claim 2, the deflection of the tool is controlled accordingto the given actual position of the drilling bit, in that a definedvalue of deflection is associated, for example in an electronic memory,with each actual position, such value being in each case transmitted tothe deflecting device of the workpiece as the control quantity.Furthermore, usefully, the given actual position is also taken intoaccount by a position control circuit.

In case the bores should additionally extend conically in thelongitudinal direction, the drilling spindle can be supported in adeflectable way. Systems suitable for such deflectability are known perse.

Schematic diagrams for a better understanding of the invention are shownin the drawing, in which:

FIG. 1 shows a schematic, perspective representation of a deviceaccording to the invention;

FIG. 2 shows a schematic representation of the patterns of motion of thedrilling bit and a workpiece worked by said bit.

With a precision drilling machine 1, a drilling bit 3 rigidly mounted ona spindle 2 rotates on a circular working path in the bore 4 of a pistonserving as the workpiece 5.

The workpiece 5 is rigidly chucked in a holder 6.

The spindle 2 is countersupported in a tip 7. High rigidity of thespindle is obtained in this way.

The holder 6 is supported in a stationary receptacle 8 and oscillatingin the direction of the double arrow A.

The oscillatory motion of the holder 6 is controlled as follows:

In an electronic memory 9, a shape of drilling to be produced is storedin a way such that a delection value for the oscillatory motion of theholder is associated with each actual position of the drilling bit. Inthis connection, it is basically necessary only to detect the givenactual position of the rotating drilling bit 3 by means of a transmitter10 synchronously rotating with the spindle 2 and to transmit it to themomery 9. The controlling quantity for the deflection of the oscillatingholder 6 is then derived therefrom, said quantity being transmitted to asetting drive of said holder.

With the system described above, only shapes of drilling with anapproximately oval basic shape can be drilled, i.e., a shape such inconnection with which the circumferential areas disposed transversely tothe motional direction A of the holder 6 are not variable based on theirradial spacing from the center axis of the spindle 2. Said limitationcan be cancelled in that the holder additionally also oscillates in adirection vertical to the one indicated by the double arrow A.

Usefully, the holder 6 is controlled not only based on the measuredactual positions of the drilling bit 3 and the deflection-setting valuesassociated with said positions in the memory 9, but adjusted with thehelp of a position control circuit. Such adjustment with the positioncontrol circuit is accomplished in that also the given actual positionof the holder 6 is reported to the electronic memory 9 and comparedthere with the should-be position of the holder 6 associated with therespective actual position of the drilling bit 3. The determineddeviation from an electronically preset drilling shape is then processedto a setting signal for the holder 6.

FIG. 2 shows in a very illustrating way the motion processes of thedrilling bit 3 and the workpiece 5. In the top part of said figure, thepositions of the workpiece are in each case shown at positions of thedrilling bit 3 displaced by 90 degrees with respect to a three-quarterturn of the drilling bit 3. Said positions are denoted by A to D. Thegreatest deviations from the starting position A can be seen to be inopposite directions in connection with the positions B and D. Saiddeviations each are denoted by "a" as the path distance.

In the lower part of FIG. 2, the path of oscillation of the workpiece 5is shown as a function of the rotary angle alpha of the drilling bit 3,whereby the oscillatory travel S is stated on the ordinate. Thedeflections "a" of the workpiece conforming to the positions B and D areshown enlarged in the presentation of the oscillatory path. Theamplitude of the oscillation curve, which is denoted by OV, is a measurefor the quality of the ovality of the bore.

I claim:
 1. Precision drilling machine with a drilling bit on a drillingspindle and a holder for a workpiece to be worked for drillingnoncircular bores, characterized in that the holder (6) for theworkpiece (5) oscillates in a least one direction translatorily with afrequency proportional to the given number of revolutions per minute ofthe drilling bit (3) and in a path of deflection dependent on the shapeof the bore to be drilled.
 2. Precision drilling machine according toclaim 1, characterized in that the deflection of the workpiece (5) iscontrolled as a function of the actual positions of the drilling bit (3)according to values associated with said actual positions anddetermining the shape of the bore.
 3. Precision drilling machineaccording to claim 1, characterized in that the radial spacing of thedrilling bit (3) from the center axis of the spindle (2) can beincreased or reduced during the drilling operation according to apredetermined motional pattern for the purpose of influencing thediameter of the bore drilled.